Prior Art
For years the conventional mercury thermometer has been the sole temperature indicating device which has been widely used in clinical applications for the measurement of temperature of the human body and for other temperature determinations. However, this type of thermometer has numerous disadvantages which are both inherent in its construction and obvious from its use, and nearly everyone who has had occasion to use such a thermometer is well acquainted with these disadvantages. For example, at least 3 minutes are usually required to obtain a meaningful temperature reading, and once used, it must be sterilized before its next clinical application. The breakable nature of this type of thermometer, the poisonous nature of mercury, the high cost per unit and the care required in packaging, shipping and storage of these thermometers are only few of their disadvantages.
Various other types of thermometers have heretofore been proposed as substitutes for the conventional mercury thermometer. For example, U.S. Pat. No. 3,465,590 issued Sept. 9, 1969 (L. A. Kluth et al.) describes a thermometer which is disposable after a single application and does not employ mercury as the thermally responsive substance. Rather, Kluth et al. employ mixtures of certain of the even series of saturated fatty acids, e.g., myristic acid, palmitic acid and lauric acid for indication of temperature of the human body within 1/2.degree. Fahrenheit. Although the use of such thermometers obviates some of the deficiencies of the conventional mercury thermometers, their application is limited to temperature measurements in the range of 96.degree. to 101.degree.F. and its accuracy is restricted to 1/2.degree. Fahrenheit, thus precluding them from use for more precise temperature measurements and, as a practical matter, they do not provide accurate clinical information regarding the temperature of the human body during a period of fever when the temperature is frequently above 101.degree. Fahrenheit, and is sometimes as high as 103.degree. or even 105.degree. Fahrenheit. Another difficulty with this thermometer is that accurate temperature determination depends upon complete change of state of the solid solution employed as the thermally responsive material. A complete change of state, i.e., from opaque solid to translucent liquid is necessary for a meaningful temperature reading in the thermometer described in the aforementioned patent.
Another type of temperature indicating device is disclosed in U.S. Pat. No. 3,175,401 issued Mar. 30, 1965 (D. E. Geldmacher). This thermometer is provided with several cavities each containing a different thermally indicating composition melting at a different temperature range. Each of the thermally indicating compositions employed by Geldmacher is normally opaque below a certain temperature and become transparent above a certain temperature. Once again, however, as in the Kluth et al. patent, temperature indication is obtained by complete change of state of the thermally responsive material in each cavity. Furthermore, as many as 40 to 50 different chemical compounds will be necessary to cover the desired clinical temperature range. While this patent discloses the use of a mixture of dichlorobenzene and diphenyl, it is noted that dichlorobenzene is merely added to lower the melting temperature of diphenyl. See column 1, lines 15-22 and FIG. 9. Additionally, as will hereinafter be explained, these two compounds, i.e., dichlorobenzene and diphenyl do not form a solid solution of the type encompassed within the scope of this invention.
Still another type of thermometer is described by P. Finkelstein in U.S. Pat. No. 3,521,489 issued July 21, 1970. The temperature indication in this type of thermometer is based upon the flow of a melted material from so-called "holding compartment" into a so-called "flow-inducing receiving element" such as an absorbent material, by a capillary action. See column 1, lines 61-72. As in the Geldmacher patent, however, temperature indication is realized by the use of numerous different thermally responsive chemical compounds, each undergoing a complete change of state at a different predetermined temperature.
There are other types of thermometers which have been suggested as replacements for the conventional mercury thermometer. For example, electronic thermometers have been proposed for this purpose. The temperature detecting elements in this type of thermometers consist of wire probes covered by disposable sheaths. However, such electronic thermometers are generally bulky and cost in the order of several hundred dollars per unit. Also, they require periodic recharging, calibration, servicing and frequent sterilization.
Thus, despite all efforts to provide a more suitable thermometer, the conventional mercury thermometer continues to dominate this field and is still the most prevalent and widely used temperature indicating device in the home and in the various institutions such as hospitals and medical and industrial laboratories